1. Field of the Invention
The present invention relates to an endoscope system and an endoscopic image processing apparatus which output endoscopic images subjected to a color correction process and, more particularly, to an endoscope system and an endoscopic image processing apparatus which perform the color correction process using more than six color axes in a color space.
2. Description of the Related Art
Endoscope systems are widely used to observe a target in an object under examination which does not lend itself to direct visual inspection by a surgeon. In the field of medicine, diagnosis is carried out based on endoscopic images shot under irradiating light from a light source device by an image pickup unit of an endoscope inserted into a body of a subject that is an object under examination. Color reproduction of endoscopic images, i.e., the extent to which original colors are reproduced faithfully, is important because of a great impact the color reproduction can have on diagnostic results. Therefore, a color correction process is performed on a video signal in an image processing unit of a processor connected with the endoscope.
As a color tone correction scheme which provides good color reproduction, an independent 6-color color-tone correction scheme is known. The independent 6-color color-tone correction scheme adjusts chroma and hue, i.e., performs a color correction process, which is color tone adjustment, with respect to each of hue regions partitioned by reference color axes (hereinafter also referred to as “reference axes” or “color axes”) of six colors—R (red), M (magenta), B (blue), C (cyan), G (green), and Y (yellow)—without changing white balance, i.e., without adding color to an achromatic-color signal. The phrase “with respect to each of hue regions,” as referred to herein, means that only two hue regions on both sides of a given color axis is affected.
However, with the independent 6-color color-tone correction scheme, although colors close to any of six colors R, M, B, C, G, and Y can be adjusted effectively, intermediate colors therebetween cannot be adjusted sufficiently.
On the other hand, in order to make fine corrections of intermediate colors as well, a color correction apparatus proposed in Japanese Patent Application Laid-Open Publication No. 9-247701 further divides colors and performs a color correction process with respect to each of color spaces resulting from division by seven color axes made up of six reference color axes corresponding to the six colors in a color space and an auxiliary color axis between an R axis and a Y axis.
Also, a color correction apparatus proposed in Japanese Patent Application Laid-Open Publication No. 2001-61160 further divides colors and performs a color correction process using 12 color axes made up of six reference color axes corresponding to the six colors in the color space and six additional reference color axes established between each pair of reference color axes.
Medical endoscope systems use various types of endoscope and light source device according to purposes. Also, endoscopic images vary greatly in color tone depending on the type of observed site. Moreover, even the same site shows substantial change in color tone if, for example, bleeding occurs. Besides, when carrying out diagnosis based on comparison with endoscopic images shot in the past, it is preferable to use endoscopic images of the same color tone as the past endoscopic images. Furthermore, each surgeon has a taste in color tones, and processing conditions for a color correction process need to be adjusted to suite the taste of the surgeon before use.
Endoscope systems which have been put to practical use include an endoscope system which operates in a normal-light imaging mode, obtains endoscopic images by shooting tissue in a living body using normal light such as white color as irradiating light, and displays the obtained endoscopic images on a monitor or the like for observation.
An endoscope system which operates in a special-light imaging mode to obtain endoscopic images by taking shots using special light as irradiating light makes it easier to distinguish between normal tissue and diseased tissue such as a tumor. For example, an endoscope system of narrow band imaging mode is used, where the narrow band imaging mode uses irradiating light whose spectral transmittance characteristics have a narrowed bandwidth. Furthermore, an endoscope system of auto fluorescence imaging mode is known, where the auto fluorescence imaging mode photographs fluorescence produced when an observed site is irradiated and exited with excitation light from a light source. The endoscope system of the auto fluorescence imaging mode uses a technique for shooting an oncotropic fluorescent substance administered to an observed site or a technique for shooting auto fluorescence which naturally occurs in a living body. Incidentally, functions of the endoscope system of the normal-light imaging mode and functions of the endoscope system of the special-light imaging mode can be implemented in a single endoscope system by changing wave length of the irradiating light supplied from the light source device.